"Hey, lowlife", Fallon greets Colbert.
"Well, that's not right", Colbert replied.
Colbert then brings the redheaded host into the video chat, where they catch him mid-shave.
The sketch aimed at Trump comes a day after the president made remarks about Fallon, Colbert and ABC's late night host Jimmy Kimmel at a rally in SC.
O'Brien then joins the conversation, unaware that Trump was even elected president.
On Colbert's show, the short video opened with Colbert writing a joke and congratulating himself - "Great monologue!" - before answering a video call from Fallon.
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Fallon has taken many potshots at the American president. "He's lost, he looks like a lost soul".
Fallon filled Colbert in on Trump's speech: "I heard he said we're all no-talent, lowlife, lost souls". Fallon was criticized by liberals for playfully ruffling Trump's hair, a moment he publicly said he regretted, causing Trump to tweet the insult "be a man", to the late show host.
Interested in Donald Trump? "He's the president! What are you doing?"
"Not so good", Colbert, says. "Well, guys, give him time!" was O'Brien's tongue-in-cheek response.
The location: The Red Hen, the Lexington, Virginia, restaurant whose owner asked Trump press secretary Sarah Huckabee Sanders to leave because the kitchen and wait staff refused to serve her.
He is also seen exhorting his competitors "be civil", adding: "If we're not careful, this could start to get ugly". "You're the president. Why are you tweeting at me?"